1. Field of the Invention
The present invention relates to a flow control valve and to a flow control system which uses the same, more particularly relates to a flow control valve which is provided with a function of enabling change to a predetermined fluid flow amount (flow rate) and of maintaining the fluid flow amount constant after change and to a flow control system which is provided with that flow control valve.
2. Description of the Related Art
In the process of production of semiconductors, the surface of a silicon wafer (substrate) is cleaned by a diluted chemical. This is aimed at removing particles and metal contaminants, oxide films, etc. A treatment solution which is obtained by mixing a plurality of types of chemicals and pure water by a suitable ratio is used. For the treatment solution, APM (ammonia/peroxide mixture, containing ammonium hydroxide, hydrogen peroxide, and pure water), HPM (hydrochloric/peroxide mixture, containing hydrochloric acid, hydrogen peroxide, and pure water), DHF (dilute hydrofluoric acid, containing hydrofluoric acid and pure water), SPM (sulfuric/peroxide mixture, containing sulfuric acid and hydrogen peroxide), etc. may be mentioned. For example, when this cleaning treatment is performed at a single wafer type system, the treatment solution etc. are supplied to the surface of a spinning wafer which is held horizontally.
In single wafer type cleaning systems, there are a cabinet type where the mixed treatment solution is stored in a tank and the treatment solution is supplied to the wafer and an in-line mixing type where a treatment solution which is mixed right in before the wafer is directly supplied. Such a latter system has a fluid mixing part. Pipes through which a high concentration chemical (concentrate) and pure water flow are connected to it whereby a mixed solution is prepared. In a single wafer type system which treats one wafer at a time, the mixed solution which is supplied to the wafer surface is small in amount. When using the in-line type, the chemical which is supplied to the mixing part is small in amount. For example, if producing DHF, the ratio of flow amounts of hydrofluoric acid and pure water is 1:100. If the flow amount of pure water is set to 2.0 liter/min, the flow amount of hydrofluoric acid required becomes 0.02 liter/min. In treatment requiring control of such a fine amount of chemical, a slight change in the flow amount ends up causing a large difference in the cleaning effect. For this reason, constant flow valves which can supply a mixing part with a chemical and pure water with a high precision become necessary.
Further, in semiconductor production, larger scale integration and finer processing are being pursued. In the International Technology Roadmap for Semiconductors (ITRS), achievement of a 24 nm process is targeted for 2014. The target figure which is expressed by this process (24 nm) is defined as half of the narrowest pitch of lines at the bottommost layer in an MPU (line width+line interval) (half pitch). With a line width set in this way, fine contaminants (particles) enter the flow path of the fluid in the semiconductor production process and have a large effect on the product yield. The particles have to be made one-quarter of the line pitch (in the case of the process for 2014, 12 nm) or less. Members which maintain the cleanliness of the fluid while causing it to flow have great meaning.
In the constant flow valve which is disclosed in U.S. Pat. No. 6,805,156B2, a plurality of diaphragms which are arranged coaxially are configured so as to move together with respect to the pressure of the controlled fluid. At a valve seat, which is present at an inflow part side, a valve element which moves together with the diaphragms operates to open and close the valve. Due to these, the differential pressure in the constant flow valve is adjusted whereby the amount of outflow of the controlled fluid can be controlled to a predetermined flow amount. Further, the flow structure keeps the controlled fluid from pooling, enables the differential structure to be simply adjusted, and enables good response.
However, when controlling flow in the range of small flow amounts (rates), it is necessary to make the valve element advance and retract by a slight valve lift (opening degree). In such a constant flow valve, a plurality of diaphragms are linked by a shaft part, and the shaft part is inserted to the inside of the flow path at which the valve seat is formed. For this reason, operation of the valve element at the time of control is liable to cause the valve seat and valve element to slide against each other.
In the flow control system which is disclosed in US 2007/0056640A1, when a change of pressure occurs at the primary side fluid, the first pressure control valve part enables the secondary side of the first pressure control valve part to be maintained at the predetermined pressure and the flow amount to be controlled. On the other hand, if pressure fluctuation occurs at the secondary side fluid, the second pressure control valve part enables the primary side of the second pressure control valve part to be maintained at the predetermined pressure and the flow amount to be controlled. Therefore, even if a change of pressure occurs at the primary side or secondary side of the flow control system, it is possible to realize a stable of fluid flow amount at a high precision.
However, in the above flow control system, if the outflow of fluid is stopped etc. at the secondary side, the fluid pressure inside the flow control system will rise. At that time, the first pressure control valve part is liable to rapidly close, whereby the valve element is liable to strongly strike the valve seat of the first pressure control valve part.
In a conventional constant flow valve or flow control system, due to the above such operations, there is a concern over the possibility of the valve seat and the valve element etc. unexpectedly contacting and generating fine particles. For this reason, a device is sought which can supply fluid by a small flow amount at a high precision and which can maintain a high cleanliness.
Furthermore, if it were possible to satisfy the above demands and change a setting to a desired flow amount and possible to maintain a constant flow amount even after the above change, there could be progress in consolidation of devices. In particular, if there were a device which realized a constant flow amount in the range of small flow amounts and control of the flow amount itself, the feed of fluid could be made even easier to manage than before and, further, the cleanliness of the fluid could be maintained better. Therefore, a new device which realizes a constant flow amount in a fluid flow amount and control of the flow amount itself within a single device has been demanded.
As related art, see the above U.S. Pat. No. 6,805,156B2 (corresponding to Japanese Patent No. 4022438 and EP 1321841B1) and US 2007/0056640A1 (corresponding to Japanese Patent Publication No. 2007-102754A).